Heat treatment method for a silicon monocrystal wafer and a silicon monocrystal wafer

ABSTRACT

There is disclosed a heat treatment method for a silicon monocrystal wafer comprising the steps of heat-treating in a reducing atmosphere a silicon monocrystal wafer manufactured by growing a silicon monocrystal ingot by Czochralski method wherein a wafer obtained from a silicon monocrystal ingot having oxygen concentration of 16 ppma or less which is manufactured by pulling at a growth rate of 0.6 mm/min or more, and in which COPs exist in high density is subjected to anneal heat treatment at 1200° C. or above for one second or more through use of a rapid heating/rapid cooling apparatus, or at 1200° C. or above for 30 minutes or more through use of a batchwise heat treatment furnace, and no defect silicon monocrystal wafer obtained with the method.  
     There can be manufactured a silicon monocrystal wafer in which crystal defects existing on the surface of the wafer or at the surface layer portion thereof are minimized, and there can be provided a silicon monocrystal wafer for a device which is excellent in electric characteristics such as oxide dielectric breakdown voltage and electrical reliability.

BACKGROUD OF INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a heat treatment method for asilicon monocrystal wafer obtained by slicing a silicon monocrystalingot grown by a Czochralski method (hereinafter referred to as “CZmethod”), and a silicon monocrystal wafer wherein crystal defect densityis significantly reduced by the method.

[0003] 2. Description of the Related Art

[0004] As a method for eliminating crystal defects of a siliconmonocrystal wafer, there has been adopted a method in which a wafer issubjected to hydrogen anneal at a high temperature. In this method,oxide precipitate is intentionally reduced with hydrogen and dissolved,and thus surface oxide-film is eliminated, resulting in increasingoxygen out-diffusion speed, so that defects can be eliminated. However,it is known that even if the hydrogen anneal is performed under thetypical condition that a temperature is 1200° C. and treatment time is60 minutes, since crystal defects and oxide precipitates remain near thesurface of the wafer, oxygen is continuously out-diffused from inside tooutside, and oxide precipitates are re-formed. Further, this methodstrongly depends on history of crystal before hydrogen anneal treatment,and therefore the wafer having less crystal defects has been selected asa wafer which is to be subjected to hydrogen anneal treatment.

[0005] As an another method, there has been adopted a method in whichcrystal defects are eliminated by lowering a growth rate of monocrystal.However, according to this method, although the number of crystaldefects can be decreased, electronic characteristics such as oxidedielectric breakdown voltage of a device are degraded since the size ofthe defect is increased.

[0006] As described above, it is difficult to eliminate crystal defectssufficiently, even when the silicon monocrystal wafer is subjected tohydrogen anneal. Furthermore, lowering the pulling rate results inincrease of the defect size, and therefore it is difficult to eliminatedefects with hydrogen anneal.

[0007] Meanwhile, COPs (Crystal Originated Particles) have recently beencited as a cause of decreasing the yield of a device-fabricatingprocess. COP is one type of crystal defects that are introduced in acrystal during the growth thereof and is known to be a defect of vacancytype having a regular octahedron structure void or cavity.

[0008] When a silicon wafer having COPs subjected to mirror-polishing iscleaned through use of a mixture solution of ammonia and hydrogenperoxide, pits are formed in the wafer surface. When the number ofparticles on the wafer is measured through use of a particle counter,pits are also detected and counted as particles together with realparticles. The thus-detected pits are called “COPs” in order todistinguish them from the actual particles.

[0009] COPs existing at the surface layer portion of a wafer degrade theelectric characteristics of the wafer. For example, a time dependentdielectric breakdown (TDDB) of oxide film, one important electriccharacteristic of a semiconductor device determined through areliability test, is known to be related to COPs, and thereforereduction of COPs is required in order to improved the time dependentdielectric breakdown.

[0010] Also, COPs are said to affect an ordinary time zero dielectricbreakdown (TZDB) of oxide film.

[0011] Moreover, COPs are said to adversely affect thedevice-fabricating process. For example, if COPs exist at the surfacelayer portion of a SOI (Silicon On Insulator) wafer, buried oxide filmis etched by etchant or atmosphere gas passed through the COPs during anetching process or a heat treatment process, and a step is formed duringa wiring process, and the thus-formed step causes breakage of wiring,resulting in a decrease in yield.

[0012] A hydrogen anneal is known as a method for reducing the COPs.However, even if anneal is conducted under the typical treatmentcondition, COPs at the surface layer portion of the wafer can not becompletely eliminated, but partly remain. Furthermore, COPs also remainat relatively near area to the surface.

[0013] The reason of why COPs at the surface layer portion of the wafercan not be completely eliminated is, for example, that COPs remain inthe wafer even when high temperature hydrogen anneal is conducted at1200° C., for 60 minutes, and later, internal COPs come to appear on thesurface as a result of that the surface is etched during hydrogenanneal. COPs which come to appear on the surface right before thetemperature begins to be lowered are difficult to be eliminated whilethe temperature is falling, and the COPs which come to appear on thesurface while the temperature is falling are more difficult to beeliminated. In order to prevent COPs from appearing while thetemperature is falling, it is necessary to raise the temperature fallingrate.

[0014] Because, silicon is generally etched in a thickness of about 0.5μm through hydrogen anneal at 1200° C. for 60 minutes, and etching ratedecreases and migration on the surface of the silicon get small, astemperature lowers. And therefore, COP appearing on the surface whilethe temperature is lowering is not etched, and is difficult to beeliminated.

[0015] Alternatively, in order to reduce COPs, it is necessary toprepare a wafer having COPs which can be easily eliminated by hydrogenanneal, and for that purpose, it is necessary to study thoroughly thecondition for pulling silicon monocrystal ingot which is to be used forpreparation of a wafer. In the prior art, a growth rate of monocrystalis lowered in order to reduce defects such as COP. However, in thiscase, although the number of COP can be decreased, the size thereof getslarge, and therefore, the probability that COPs are not eliminated ishigh even if the wafer prepared from the monocrystal ingot thus obtainedis subjected to hydrogen anneal. Therefore, it is difficult to eliminateCOP defects by the existing technique.

SUMMARY OF THE INVENTION

[0016] The present invention has been accomplished to solve theabove-mentioned problems, and an object of the present invention is tomanufacture a silicon monocrystal wafer in which crystal defectsexisting on the surface of the wafer or at the surface layer portionthereof are minimized, and to provide a silicon monocrystal wafer for adevice which is excellent in not only oxide dielectric breakdown voltagebut also other electric characteristics such as electrical reliability.

[0017] Another object of the present invention is to enable productionof a silicon monocrystal wafer having no defect, and to achieveenhancement of productivity, reduction in the amount of hydrogen to beused, cost reduction, and the like.

[0018] To achieve the above object, the present invention relates to aheat treatment method for a silicon monocrystal wafer comprising thesteps of heat-treating in a reducing atmosphere a silicon monocrystalwafer manufactured by slicing a silicon monocrystal ingot which is grownby Czochralski method wherein a wafer obtained by slicing a siliconmonocrystal ingot having oxygen concentration of 16 ppma or less whichis manufactured by pulling at a growth rate of 0.6 mm/min or more, andin which COPs exist in high density is subjected to anneal heattreatment at 1200° C. or above for one second or more through use of arapid heating/rapid cooling apparatus.

[0019] The rapid heating/rapid cooling means, for example, a method thata wafer is immediately loaded into a heat treatment furnace in which atemperature is arranged in the above-mentioned range, and is immediatelyloaded out upon elapse of the above-mentioned heat treatment time, or amethod that a wafer is immediately subjected to heat treatment with alump heater or the like after it is arranged at a predetermined positionin the heat treatment furnace. The language reading “immediately loadedinto” or “immediately loaded out” means that there are not performed anoperation for raising and lowering the temperature over a certainperiod, as well as a conventional so-called loading or unloadingoperation in which a wafer is slowly loaded into the heat treatmentfurnace and slowly loaded out. Of course, it takes a certain time tobring a wafer to a predetermined position in the furnace, for example,several seconds to several minutes depending on capability of a transferapparatus for loading of a wafer. The apparatus having theabove-mentioned function is called a rapid thermal annealer (hereinafterabbreviated to “RTA apparatus”).

[0020] As described above, a silicon monocrystal ingot having an oxygenconcentration of 16 ppma or less in which COPs exist in high density ismanufactured by pulling a silicon monocrystal ingot by CZ method at ahigh growth rate of 0.6 mm/min or more, preferably 0.8 mm/min or more.Then, the wafer obtained by slicing the silicon monocrystal ingot thusmanufactured is subjected to anneal heat treatment with a rapidheating/rapid cooling apparatus in a reducing atmosphere at atemperature of 1200° C. or above for one second or more, so that therecan be obtained the wafer in which COPs on the surface and at thesurface layer portion thereof are significantly reduced. Accordingly,there can be obtained a device that not only oxide dielectric breakdownvoltage but also other electric characteristics such as electricalreliability are significantly improved. Furthermore, a wafer having alarge diameter in which COPs is especially difficult to be reduced canbe treated in a short time, and therefore, enhancement of productivityis achieved, and safety is improved since an amount of hydrogen gas tobe used can be decreased.

[0021] The present invention also relates to a heat treatment method fora silicon monocrystal wafer comprising the steps of heat-treating in areducing atmosphere a silicon monocrystal wafer manufactured by slicinga silicon monocrystal ingot which is grown by Czochralski method whereina wafer obtained by slicing a silicon monocrystal ingot having oxygenconcentration of 16 ppma or less which is grown at a growth rate of 0.6mm/min or more, preferably 0.8 mm/min or more, and in which COPs existin high density is subjected to anneal heat treatment at 1200° C. orabove for 30 minutes or more through use of a batchwise heat treatmentfurnace.

[0022] A batchwiseheat treatment furnace means a furnace in which a heattreatment is performed in a so-called batchwise operation, that is,plural wafers are placed on plural shelves provided in the vertical typeheat treatment furnace, hydrogen gas is then introduced therein,temperature in the furnace is raised relatively slowly, and then heattreatment is performed at a predetermined temperature for apredetermined period, followed by lowering the temperature relativelyslowly. When using the batchwise furnace, a large amount of wafers canbe subjected to heat treatment. However, one cycle additionallyincluding time for loading in and loading out of the wafer is long, andtherefore productivity is not so excellent as that of RTA apparatus.However, it is excellent in controllability of temperature so thatstable operation can be achieved.

[0023] When the wafer manufactured from the silicon monocrystal ingothaving the similar quality to one of the ingot used in the abovedescribed method using a rapid heating/rapid cooling apparatus issubjected to anneal heat treatment using the batchwise heat treatmentfurnace at the temperature of 1200° C. or above, for 30 minutes or more,COPs on the surface and at the surface layer portion thereof aresignificantly reduced, electric characteristics of the device such asoxide dielectric breakdown voltage, electrical reliability or the likeare significantly improved. Furthermore, as for a wafer having largediameter, enhancement of productivity and cost reduction are achieved.

[0024] In this case, COPs existing in high density in a siliconmonocrystal to be subjected to the heat treatment preferably have a sizeof 60-130 nm, and preferably consist of only one void.

[0025] The silicon monocrystal in which such a fine COPs exist in highdensity can be easily manufactured by pulling at 0.6 mm/min or more,preferably 0.8 mm/min or more. Furthermore, when monocrystal has oxygenconcentration of 16 ppma or less, almost no oxide film exists in theinner wall of COP, and therefore, COPs can be eliminated quite easilywith hydrogen anneal heat treatment of the wafer.

[0026] Furthermore, oxygen concentration in the monocrystal can becontrolled by adjusting a rotating number of a crucible containingsilicon melt therein as a raw material, a rotating number of a growingmonocrystal, quantity of flow of inert gas, temperature of melt, or thelike.

[0027] The present invention also relates to a heat treatment method ofa silicon monocrystal wafer wherein the silicon wafer having COPs of asize of 60-130 nm is subjected to heat treatment in a reducingatmosphere at a temperature of 1200° C. or above. Furthermore, thepresent invention relates to a heat treatment method of a siliconmonocrystal wafer wherein the silicon wafer wherein COP is crystaldefect consisting of only one void is subjected to a heat treatment in areducing atmosphere at a temperature of 1200° C. or above.

[0028] Such a fine COP, or COP which is crystal defect consisting ofonly one void can be easily eliminated by high temperature heattreatment in a reducing atmosphere, regardless of a method formanufacturing a wafer.

[0029] In an embodiment, when the above mentioned reducing atmosphere is100%-hydrogen atmosphere, or a mixed atmosphere of hydrogen and argon,sufficient effect of hydrogen anneal heat treatment can be obtained,COPs having oxide film on the inner wall can be significantly decreased,and a void can be filled with silicon, so that almost no defect wafercan be provided.

[0030] Furthermore, the present invention relates to a siliconmonocrystal wafer in which COPs are eliminated by the method describedabove.

[0031] In the silicon monocrystal wafer manufactured by the heattreatment method described above, since the size of COP is small, oxidefilm on the inner wall of COP can be reduced and dissolved by hydrogensurely diffused from the surface of the wafer thereto by hydrogenanneal, a void can be filled with silicon supplied from the surface ofthe wafer to be eliminated, and thus COPs can be eliminated, so thatactually no defect silicon monocrystal wafer can be provided.Accordingly, characteristics of a device is improved, yield is improved,so that quite useful silicon monocrystal wafer can be provided.

[0032] According to the present invention, a wafer obtained by slicing asilicon monocrystal ingot having oxygen concentration of 16 ppma or lesswhich is manufactured by pulling at a growth rate of 0.6 mm/minormore,and in which COPs exist in high density is subjected to high temperatureheat treatment in a reducing atmosphere through use of a rapidheating/rapid cooling apparatus or a batchwise heat treatment furnace,so that COPs on the surface and at the surface layer portion can besignificantly reduced and thus the no defect wafer can be manufactured.Accordingly, the wafer is quite valuable as a wafer for a device whichis excellent in electrical characteristics. Furthermore, especially fora large diameter wafer, since high speed pulling can be performed, it ispossible to achieve enhancement of productivity and cost reduction byselecting the monocrystal growing condition and hydrogen annealcondition appropriately. Moreover, reduction in the amount of hydrogento be used can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033]FIG. 1 is a graph showing the relationship between heat treatmenttemperature and the number of LPD (COP) on the surface of the waferafter hydrogen anneal heat treatment by the rapid heating/rapid coolingapparatus;

[0034]FIG. 2 is a graph comparing LPD (COP) (number/wafer) at thesurface layer portion of the wafer before and after hydrogen anneal ineach pulling condition of the silicon monocrystal;

[0035]FIG. 3 is a graph showing a hydrogen anneal condition andcomparison of the effect of hydrogen anneal with RTA apparatus with thatwith a batchwise heat treatment furnace;

[0036]FIG. 4 is a graph comparing the number of LPD(COP) at the surfacelayer portion of the wafer obtained by subjecting to hydrogen annealwith a RTA apparatus and a batchwise apparatus;

[0037]FIG. 5 is a schematic view showing the step that the twin typevoid is growing;

[0038]FIG. 6 is a schematic view showing an example of a heat treatmentfurnace which can heat and cool a silicon wafer rapidly.

DESCRIPTION OF THE INVENTION AND A PREFERRED EMBODIMENT

[0039] The present invention will be further described below in detail,but is not limited thereto.

[0040] The present inventors carried out various experiments and studiesto find heat treatment conditions that can reduce the density of COPsexisting at the surface layer portion of a silicon wafer, and found thatwhen a monocrystal ingot in which fine COPs exist in high density ismanufactured by pulling a monocrystal having low oxygen concentration athigh speed, and then the resultant wafer is subjected to hydrogenanneal, COP density is significantly lowered, so that no defect siliconmonocrystal wafer can be obtained. The present invention wasaccomplished based on this finding.

[0041] Basic idea about the present invention is based on the followingfindings.

[0042] Namely, Laser Scattering Tomography Defect (LSTD) in the siliconmonocrystal pulled under a general condition in CZ method was previouslyobserved with a transmission electron microscope (TEM), and it wasreported that COP had a shape that two or three of regular octahedralvoids surrounded by thin oxide film having a thickness of 2-4 nm werelinked, and had a size of 100-300 nm (M. Kato et al.; Jpn. Appln. Pys.35 (1996) 5597).

[0043] However, further studies have revealed that there exists only oneindependent single type defect, when LSTD in CZ crystal cooled rapidlyis observed. The single type defect is also a regular octahedral voidsized 60-130 nm. The oxide film is thinner than that obtained by generalcooling as in the above-mentioned conventional method, or does not existin some cases.

[0044] Furthermore, it has been found that the single type defectsgenerate at an early stage of defect growing, and twin or triplet typedefects generate in the subsequent stage.

[0045]FIG. 5 is a schematic view showing the step that the twin typevoid is growing. In the cooling step of a growing monocrystal, first,vacancy 20 begin to aggregate to form a fine void as shown in (a). Then,the void absorbs vacancy which is diffused thereto, and grows whileinterstitial oxygen 21 gathers around the void to form thin oxide film22 as shown in (b). The oxide film surrounds the void, and prevents thevacancy from being absorbed therein as shown in (c) and (d). Then, thevacancy begins to attack the weakest site of the oxide film to make thedefect grow. Then, at the weakest site, the second void 23 begins to bedistended to form the twin type void as shown in (e).

[0046] The difference between the condition for forming void of singletype and that for forming twin or triplet type void is as follows. Whenthe crystal is pulled at high speed and cooled rapidly, a lot of smallsingle type voids are formed. In this case, oxide film at inner wall ofCOP is quite thin or does not exist when oxygen concentration is low.When the crystal is pulled at low speed and cooled slowly, smallernumber of twin or triplet type voids are formed. In that case, the oxidefilm at the inner wall of COP tends to be thick.

[0047] Further analysis of the above phenomenon revealed the followings.In the past, it is attempted to decrease defects such as COPs and thelike by growing monocrystal at low speed, and subjecting a wafer tohydrogen anneal to eliminate remaining large twin or triplet type COPdefects. However, it is difficult to eliminate the COPs with hydrogenanneal, since the COPs are too large, and the thick oxide film exists onthe surface of the COP. On the contrary, according to the presentinvention, monocrystal having low oxygen concentration is grown at highspeed to provide a monocrystal ingot in which there exist a lot ofsingle type COP having no oxide film or thin oxide film if any. In thatcase, COP can be easily eliminated completely with a heat treatment,namely hydrogen anneal of the wafer.

[0048] According to the present invention, the pulling rate is 0.6mm/min or more, preferably 0.8 mm/min or more, so that a lot of singletype COPs having small size as 60-130 nm can generate, and growing tothe twin or triplet type COP can be well prevented. Therefore, thepulling rate is preferably as fast as possible, for example 1.0 mm ormore, depending on the diameter of the pulled crystal. If the pullingrate is less than 0.6 mm, the crystal is cooled too slowly, andtherefore COPs grow to the twin type or triplet type and the oxide filmat the inner wall of COP get harder, although the number of COPs isdecreased. The single type COP has a size of approximately 60-130 nm,and has no oxide film at the inner wall in most cases when the oxygenconcentration is low.

[0049] Oxygen concentration in the silicon monocrystal ingot ispreferably up to 16 ppma (JEIDA: Japan Electronic Industry DevelopmentAssociation), especially up to 10 ppma. When oxygen concentration ismore than 16 ppma, oxide film gets thick, resulting in insufficientelimination of COPs in the hydrogen anneal step, and longer heattreatment time, which may affect adversely on the quality andproductivity of the wafer.

[0050] Oxygen concentration in the silicon monocrystal ingot can becontrolled easily by conventional methods, for example, by adjustingquantity of flow of inert gas, rotating number of crucible, a rotatingnumber of a growing monocrystal, temperature of silicon melt, or thelike.

[0051] Subsequently, a silicon wafer is produced by slicing the abovementioned silicon monocrystal, and subjecting it to a heat treatmentwith a rapid heating/rapid cooling apparatus (RTA apparatus) or abatchwise apparatus in a reducing atmosphere of 100% hydrogen or a mixedatmosphere of hydrogen and argon at 1200° C. or above for one second ormore in the case of a RTA apparatus or for 30 minutes or more in thecase of the batchwise apparatus, so that COP density is significantlydecreased. Especially the COP density can be decreased to zero by thiscondition. When the wafer subjected to above described hydrogen annealis used, there can be produced a device which is excellent in not onlyoxide dielectric breakdown voltage but also other electriccharacteristics such as a time dependent dielectric breakdown.

[0052] An embodiment of the present invention will now be described withreference to the drawings. However, the present invention is not limitedthereto.

[0053] Examples of an apparatus which can heat and cool a silicon waferrapidly used in a hydrogen anneal step of the present invention include:heater such as a lamp heater with heat radiating, a laser heater with alaser beam, a X-ray heater using X-ray, a resistance heater. An exampleof commercially available apparatuses is SHS-2800 (product of ASTcorp.). These apparatuses are neither extremely complicated norexpensive.

[0054] First, a description will be given of rapid heating/rapid coolingapparatus used in the present invention. FIG. 6 is schematic sectionalview of a resistance heating type rapid heating/rapid cooling apparatus.

[0055] A heat-treatment furnace 10 shown in FIG. 6 includes a bell jar 1which is formed from, for example, silicon carbide or quarts and inwhich a wafer is heat-treated. Heaters 2 and 2′ surround the bell jar 1so as to heat the bell jar 1. The heater 2′ is separated from the heater2 along a vertical direction. Also, power supplied to the heater 2′ isindependent of that to the heater 2 for independent power controlbetween the heaters 2 and 2′. The heating method is not limited thereto,but so-called radiation heating and induction heating may also beapplicable. The bell jar 1 and the heaters 2 and 2′ are housed in ahousing 3 serving as a heat shield.

[0056] A water-cooled chamber 4 and a base plate 5 are arranged at thelower portion of a furnace so as to isolate the interior of the bell jar1 from the atmosphere. A wafer 8 is held on a stage 7, which is attachedto the top end of a support shaft 6, which, in turn, is moved verticallyby means of a motor 9. In order to load a wafer into or unload from thefurnace along a horizontal direction, the water-cooled chamber 4 has anunillustrated wafer port which is opened and closed by means of a gatevalve. A gas inlet and a gas outlet are provided in the base plate 5 sothat the gas atmosphere within the furnace can be adjusted.

[0057] In the heat treatment furnace 10 having the abovedescribedstructure, heat treatment for rapid heating/rapid cooling of a siliconwafer is carried out in the procedure described below.

[0058] First, the interior of the bell jar 1 is heated to a desiredtemperature of 1200° C. or above by the heaters 2 and 2′ and is thenheld at the desired temperature. Through mutually independent control onpower supplied to the heaters 2 and 2′, a temperature distribution canbe established within the bell jar 1 along a vertical direction.Accordingly, the heat-treatment temperature of a wafer is determined bythe position of the stage 7, i.e. the amount of insertion of the supportshaft 6 into the furnace.

[0059] In a state in which the interior of the bell jar 1 is maintainedat a desired temperature, a wafer is inserted into the water-cooledchamber 4 through the wafer port by an unillustrated wafer handlingapparatus arranged next to the heat treatment furnace 10. The insertedwafer is placed in, for example, a SiC boat provided on the stage 7which is situated at the bottom standby position. Since the water-cooledchamber 4 and the base plate 5 are water-cooled, the wafer located atthis standby position is not heated to a high temperature.

[0060] Upon completion of placing the wafer on the stage 7, the motor 9is immediately driven to insert the support shaft 6 into the furnace sothat the stage 7 is raised to a shaft 6 into the furnace so that thestage 7 is raised to a heat treatment position where a desiredtemperature in the range of 1200° C. or above is established, therebyheat-treating the wafer at the temperature. In this case, since onlyapproximately 20 seconds, for example, is required for moving the stage7 from the bottom standby position in the wafer-cooled chamber 4 to theheat treatment position, the silicon wafer is heated quickly.

[0061] The stage 7 is halted at the desired temperature position for apredetermined time (one second or more), thereby subjecting the wafer tohigh-temperature heat treatment over the halting time. Upon elapse ofthe predetermined time to complete high-temperature heat treatment, themotor 9 is immediately driven to withdraw the support shaft 6 from theinterior of the furnace to thereby lower the stage 7 to the bottomstandby position in the water-cooled chamber 4. This lowering motion canbe completed in approximately 20 seconds, for example. The wafer on thestage 7 is quickly cooled, since the water-cooled chamber 4 and the baseplate 5 are water-cooled. Finally, the wafer is unloaded from inside thewater-cooled chamber 4 by the wafer handling apparatus, thus completingthe heat treatment.

[0062] When there are more wafers to be heat-treated, these wafers canbe sequentially loaded into and heat-treated in the heat treatmentfurnace 10 maintained at a predetermined high temperature.

[0063] Through use of the above-described rapid heating/rapid coolingapparatus, silicon wafers were heat treated in a single-wafer processingscheme in a 100% hydrogen atmosphere.

[0064] The wafers used in the present embodiment were sliced in acommonly practiced manner from a silicon ingot having oxygenconcentration of up to 16 ppma in which COPs having a size of 60-130 nmexist in high density, that had been manufactured in accordance with theabove-mentioned Czochralski method at a pulling rate of 0.8 mm /min to1.2 mm/min, and were then subjected to mirror-polishing. The wafers eachhad a diameter of 8 inches and a <100> orientation.

[0065] The reducing atmosphere can be 100% hydrogen gas, or a mixedatmosphere of hydrogen and argon, the latter may be selected in order tocontrol reducing force of hydrogen, to prevent generation of slipdislocation or by the other reasons such as aspect of safety.

[0066] The heat treatment was conducted in a temperature of 1200° C. orabove for period of time one second or more. The temperature less than1200° C. is not enough to eliminate COP completely. The time less thanone second is not enough to achieve heat treatment effect.

[0067] As described above, the wafer prepared by subjecting the waferhaving small COPs to hydrogen anneal through use of RTA apparatus hasalmost no COP, especially at the surface layer portion, so that a nodefect silicon monocrystal wafer can be manufactured. Accordingly, byusing the wafer subjected to hydrogen anneal, there can be prepared adevice which is excellent in electrical characteristics such as oxidedielectric breakdown voltage, a time dependent dielectric breakdown, orthe like.

[0068] When the RTA apparatus is used, temperature is raised quiterapidly so that it takes quite short time to reach the temperature atwhich COP can be eliminated, and therefore, COPs may be eliminatedeasily even when a lot of single type COPs exist.

[0069] A batchwise heat treatment furnace can also be used for hydrogenanneal. The batch type heat treatment furnace means so called batchwiseheat treatment wherein wafers are placed in the vertical type or thehorizontal type heat treatment furnace, hydrogen gas is introducedtherein, the interior of the furnace is mildly heated, and then the heattreatment is performed at a predetermined temperature for apredetermined period, followed by descending the temperature relativelyslowly. When using the batchwise furnace, a large amount of wafers canbe subjected to the heat treatment at once. However, one cycleadditionally including time for loading in and loading out of the waferis long, and therefore productivity is not always excellent. However, itis excellent in controllability of temperature so that stable operationcan be achieved.

[0070] The condition for hydrogen anneal through use of a batchwise heattreatment furnace is basically same as that for the above-mentioned RTAapparatus, namely, in 100% hydrogen gas atmosphere or in a mixedatmosphere of argon and hydrogen, at 1200° C. or more. Heat treatmenttime is preferably 30 minutes or more. The heat treatment less than 30minutes cannot provide sufficient effect, namely, COPs cannot beeliminated sufficiently.

[0071] As described in the above, even when the batchwise vertical typeheat treatment furnace is used, there can be eliminated almostcompletely COPs at the surface layer portion of the wafer prepared bysubjecting a wafer in which small COPs exist, so that no defect siliconmonocrystal wafer can be manufactured. Accordingly, by using the wafersubjected to hydrogen anneal, there can be fabricated a semiconductordevice which is excellent electrical characteristics such as oxidedielectric breakdown voltage, time dependent dielectric breakdown, orthe like.

[0072] In the measurement by another method, total number of COPs at thesurface layer portion (from the surface of the wafer to the depth of 0.5μm) was decreased to about half an amount. Accordingly, a batchwiseapparatus or a RTA apparatus can be used depending on purpose.

EXAMPLES

[0073] The following examples and comparative examples are beingsubmitted to further explain the present invention. These examples arenot intended to limit the scope of the present invention.

Example 1

[0074] With the pulling rate (SE: seed elevation) of the siliconmonocrystal set in three stages, that is 0.6, 0.95, 1.4 mm/min, themonocrystal ingot having oxygen concentration (Oi) of 16 ppma and adiameter of 8 inches was pulled, and a wafer was prepared therefrom. Thewafer was then subjected to hydrogen anneal at a temperature of 1000 to1200° C. COPs existing at the surface layer portion of the wafer wasmeasured in LPD (Light Point Defect) mode of a light scatteringapparatus.

[0075] The results were shown in FIG. 1 and as follows: when the waferwas subjected to hydrogen anneal in 100% hydrogen atmosphere, at 1200°C., for 10 seconds through use of a RTA apparatus (SHS-2800), thenumbers of COPs of size of 0.20 to 0.12 μm at the surface layer portionof the wafer were respectively 50, 6, 2 per a wafer. Namely when thepulling rate is higher, more COPs were eliminated. When the wafermanufactured under the condition that SE (pulling rate) is 1.4 mm/min,and Oi is 16 ppma was subjected to hydrogen anneal in 100% hydrogenatmosphere, at 1200° C. for one hour with a batchwise heat treatmentfurnace, the number of COPs was 90 per a wafer.

[0076] These results show that a heat treatment is preferably performedat a temperature of 1200° C. or above, that when the wafer manufacturedby high speed pulling is subjected to hydrogen anneal, LPD(COP) defectscan be easily reduced, and therefore that the wafer having less CoPs canbe obtained. Furthermore, it is found that the pulling rate is slowerthan 0.6 mm/min, although it depends on the diameter of the pulledcrystal, COP grows too much to achieve the effect of hydrogen anneal.

Example 2

[0077] The importance is in the total number of COPs at the surfacelayer portion in depth of up to 0.5 μm which becomes a surface afterdevice fabrication affecting the device. However, it cannot be counteddirectly with a particle counter at once. Therefore, oxide film isformed in several stages of thickness by a thermal oxidation treatment,and the number of COPs in silicon is counted via the oxide film with aparticle counter to calculate an integral value in depth direction. Forexample, the oxide film was grown to the thickness of 1.0 μm in severalstages, and the total number (an integral value) of COPs existing in thedepth of up to 0.5 μm from the surface was measured (Hereinafterreferred to as “oxide film method”.

[0078]FIG. 2 shows effect of hydrogen anneal measured with COPmeasurement by the oxide film method. Silicon monocrystal was pulled ata rate of 1.4, 1.4, 0.95 mm/min to produce the wafers wherein oxygenconcentration was 16, 12, 16 ppma respectively. The resultant waferswere subjected to thermal oxidation treatment to provide samples onwhich surface an oxide (SiO₂) film having thickness of up to 0.95 μm wasformed. The number of COPs at the surface layer portion of them wascounted by the oxide film method. On the other hand, other three waferswere prepared by the same method as described above, and were subjectedto hydrogen anneal in 100%-hydrogen atmosphere, at 1200° C. for 10seconds through use of RTA apparatus. The wafers were then subjected tothermal oxidation treatment as described above to form an oxide filmhaving thickness of up to 0.95 μm. COPs at the surface layer portion ofthe wafer was measured by the oxide film method.

[0079] The results were shown in FIG. 2. In FIG. 2, LPD[COP](number/wafer) at the surface layer portion of the wafer before andafter hydrogen anneal in each pulling condition of the siliconmonocrystal is shown as a bar chart. As is clear from FIG. 2, when thepulling rate is fast as 1.4 mm/min, and oxygen concentration is 12 ppma,the largest reducing rate of the number of LPD (72%) can be achieved.Among the wafers which were not subjected to hydrogen anneal, the wafermanufactured by pulling crystal at a rate of 0.95 mm/min has the leastLPD (approximately 6200/wafer). However, in the same wafers except thatthey were subjected to hydrogen anneal , a reducing rate of the numberof LPD was the smallest (approximately 18%). These results reveals thefollowing facts. When crystal is grown slowly, the number of COPs mayget small, but the size of COP gets large, and in that case, COPs cannotbe easily reduced. On the contrary, when crystal is grown fast, thenumber of COPs may get large, but the size of COPs gets small, and inthat case, COPs can be easily reduced. When oxygen concentration is low,COPs can be easily reduced. Accordingly, it is the most effective forreducing COPs with hydrogen anneal to use the wafer having low oxygenconcentration manufactured by pulling crystal at high speed.

Example 3

[0080] The effect of hydrogen anneal with RTA apparatus is compared withthat with a batchwise heat treatment furnace.

[0081] With the pulling rate (SE) of the silicon monocrystal of 1.4mm/min, the monocrystal ingot having oxygen concentration (Oi) of 16ppma was pulled and wafers were prepared therefrom. Some of the waferswere then subjected to the hydrogen anneal at a temperature of 1200° C.for 10 seconds through use of RTA apparatus. The other of the waferswere subjected to the hydrogen anneal under the same condition for theabove anneal with RTA apparatus except that a batchwise heat treatmentfurnace was used, and a treatment period was 60 minutes. The resultswere shown in a bar chart in FIG. 3. FIG. 3 shows that when the waferwas subjected to hydrogen anneal with RTA apparatus, the number of COPsexisting at the surface layer portion of the wafer is significantlyreduced to approximately 8 number/wafer, and therefore is quiteadvantageous compared with the wafer subjected to hydrogen anneal with abatchwise heat treatment apparatus (approximately 93 number/wafer).

[0082] The effect of hydrogen anneal with RTA apparatus to COPs at thesurface layer portion of the wafer was compared with that with abatchwise heat treatment furnace through use of COPs measurement by theoxide film method. History of the wafer and hydrogen anneal conditionwere the same as those described above except that the oxygenconcentration of the wafer was 12 ppma. Heat treatment of the wafer wasconducted in the similar manner to Example 2, to grow oxide film havingthickness up to 0.95 μm, and COPs were measured.

[0083] The results were shown in a bar chart in FIG. 4. FIG. 4 showsthat when the wafer was subjected to hydrogen anneal with RTA apparatus,the number (integral value in depth direction) of LPD(COP) existing atthe surface layer portion (in depth up to about 0.5 μm) of the wafer wasapproximately 2000 number/wafer, and the number of COPs at the surfacelayer portion of the wafer subjected to hydrogen anneal with a batchwiseheat treatment furnace was 950 number/wafer. Therefore, it isadvantageous to use a batchwise heat treatment furnace as for the numberof COPs at the area in depth of up to about 0.5 μm from the surface ofthe wafer.

[0084] The present invention is not limited to the abovedescribedembodiment. The above-described embodiment is a mere example, and thosehaving the substantially same structure as that described in theappended claims and providing the similar action and effects areincluded in the scope of the present invention.

[0085] For example, in the above-described embodiment, a resistanceheating type heat treatment furnace as shown in FIG. 6 is used. However,the present invention is not limited thereto. In principle, anyapparatus may be used so long as it can heat and cool siliconmonocrystal wafer rapidly and can heat the wafers to a temperature of1200° C. or higher. For example, heat treatment can be conducted with alaser heater, X ray heater, a lamp heater, a batchwise heat treatmentfurnace.

What is claimed is:
 1. A heat treatment method for a silicon monocrystalwafer comprising the steps of heat-treating in a reducing atmosphere asilicon monocrystal wafer manufactured by slicing a silicon monocrystalingot which is grown by Czochralski method wherein a wafer obtained byslicing a silicon monocrystal ingot having oxygen concentration of 16ppma or less which is manufactured by pulling at a growth rate of 0.6mm/min or more, and in which COPs exist in high density is subjected toanneal heat treatment at 1200° C. or above for one second or morethrough use of a rapid heating/rapid cooling apparatus.
 2. A heattreatment method for a silicon monocrystal wafer comprising the steps ofheat-treating in a reducing atmosphere a silicon monocrystal wafermanufactured by slicing a silicon monocrystal ingot which is grown byCzochralski method wherein a wafer obtained by slicing a siliconmonocrystal ingot having oxygen concentration of 16 ppma or less whichis grown at a growth rate of 0.6 mm/min or more, and in which COPs existin high density is subjected to anneal heat treatment at 1200° C. orabove for 30 minutes or more through use of a batchwise heat treatmentfurnace.
 3. The heat treatment method for a silicon monocrystal waferaccording to claim 1 , wherein the size of the COP existing in highdensity in the silicon monocrystal to be subjected to said heattreatment is 60-130 nm.
 4. The heat treatment method for a siliconmonocrystal wafer according to claim 2 , wherein the size of the COPexisting in high density in the silicon monocrystal to be subjected tosaid heat treatment is 60-130 nm.
 5. The heat treatment method for asilicon monocrystal wafer according to claim 1 , wherein said COPconsists of only one void.
 6. The heat treatment method for a siliconmonocrystal wafer according to claim 2 , wherein said COP consists ofonly one void.
 7. The heat treatment method for a silicon monocrystalwafer according to claim 3 , wherein said COP consists of only one void.8. The heat treatment method for a silicon monocrystal wafer accordingto claim 4 , wherein said COP consists of only one void.
 9. A heattreatment method of a silicon monocrystal wafer wherein the siliconwafer having COPs of a size of 60-130 nm is subjected to heat treatmentin a reducing atmosphere at a temperature of 1200° C. or above.
 10. Aheat treatment method of a silicon monocrystal wafer wherein the siliconwafer wherein COP is crystal defect consisting of only one void issubjected to a heat treatment in a reducing atmosphere at a temperatureof 1200° C. or above.
 11. The heat treatment method for a siliconmonocrystal wafer according to claim 1 wherein said reducing atmosphereis 100%-hydrogen atmosphere, or a mixed atmosphere of hydrogen argon.12. The heat treatment method for a silicon monocrystal wafer accordingto claim 2 wherein said reducing atmosphere is 100%-hydrogen atmosphere,or a mixed atmosphere of hydrogen and argon.
 13. The heat treatmentmethod for a silicon monocrystal wafer according to claim 9 wherein saidreducing atmosphere is 100%-hydrogen atmosphere, or a mixed atmosphereof hydrogen argon.
 14. The heat treatment method for a siliconmonocrystal wafer according to claim 10 wherein said reducing atmosphereis 100%-hydrogen atmosphere, or a mixed atmosphere of hydrogen argon.15. A silicon monocrystal wafer in which COPs are eliminated by the heattreatment method of claim 1 .
 16. A silicon monocrystal wafer in whichCOPs are eliminated by the heat treatment method of claim 2 .
 17. Asilicon monocrystal wafer in which COPs are eliminated by the heattreatment method of claim 9 .
 18. A silicon monocrystal wafer in whichCOPs are eliminated by the heat treatment method of claim 10 .